A computer network is a collection of interconnected computing devices that exchange data and share resources. The computing devices may be interconnected by one or more links. The term “link” is often used to refer to the connection between two devices on a network and may include a physical medium, such as a copper wire, a coaxial cable, or any of a host of different fiber optic lines, or a wireless connection. Often, in highly populated areas, the computer network includes links laid in the shape of a ring. When shaped in a ring, the network is referred to as a “ring network.” A ring network in a highly populated area that implements a Layer Two (L2) Ethernet communications protocol may be referred to as a “metro Ethernet network.”
In a typical configuration, a metro Ethernet network includes a plurality of interconnected metro termination units (MTUs) that provide access to the metro Ethernet network for computing devices referred to as customer subscriber devices. The computing devices couple to the MTUs to gain access to the metro Ethernet network and thereby interconnect with other computing devices coupled to the metro Ethernet network. One or more layer three (L3) provider edge (PE) routers may couple the metro Ethernet network with a public network, such as the Internet, or other private networks. Via the PE routers, computing devices may utilize the metro Ethernet network to access the public or private networks. The MTUs within the metro Ethernet network operate as layer two (L2) devices and typically learn L2 network addresses, e.g., Media Access Control (MAC) addresses, of various network devices as the MTUs forward L2 communications (e.g., Ethernet packets also referred to as Ethernet frames) associated with the network devices. Once learned, the MTUs store the learned MAC address information to more efficiently switch L2 communications within the Ethernet network. When the MTUs receive additional packets to direct to a network device with a learned MAC address, the MTUs look up the stored MAC address information and direct the packets to the network device based on the stored information.
Operations, Administration and Maintenance (OAM) generally refers to processes, activities, tools, standards and other techniques that involve operating, administering and maintaining, e.g., troubleshooting, a computer network. The combined OAM techniques may constitute an OAM protocol. An OAM protocol, such as Connectivity Fault Management (CFM) as described in the Institute of Electrical and Electronics Engineers (IEEE) 802.1ag standard, may include a number of proactive and diagnostic fault localization procedures. For example, a network device operating in accordance with CFM may proactively transmit continuity check (CC) messages at a predetermined rate to other devices within the same maintenance association, and receive CC messages from the devices. A maintenance association is a logical grouping of devices within the network configured to verify the integrity of a single service instance. A service instance may, for example, represent a portion of a provider network that a given customer can access to query a status of services delivered for that customer. The CC messages provide connectivity verification to the other network devices within the maintenance association.
Devices and/or links of the network may fail due to any of a number of reasons. When a device or link of the network fails, the result is typically a degradation or loss of service to particular customers, which is generally undesirable. An administrator of the network would therefore like to limit the duration of the failure. One conventional approach to mitigate the effects of failure of a PE router is to utilize a “multi-homed” architecture in which two or more redundant PE routers are used to couple the metro Ethernet network with the public network. In operation, the MTU coupled the two or more redundant PE routers selects one PE router as the preferred PE router and directs data packets to the public network through the preferred PE router. However, even though only one PE router is the preferred PE router, each PE router connected to the MTU typically reserves resources for processing data packets to and from the MTU.
When an MTU is multi-homed, a network error may exist within the public network connecting the preferred PE router and a network device outside the metro Ethernet network. Conventionally, the stored MAC address information must age out before the MTU will direct the network packets over a different network path that does not include the network error. That is, the MTU continues to direct packets over a network path that includes the network error until the stored MAC address information is purged, resulting in packet loss. To minimize the number of lost or dropped packets, the PE router may make the link between the PE router and the MTU unavailable by bringing down the link or “flapping” the link between the MTU and the PE router. The PE router may “flap” the link between the MTU and the PE router by issuing a series of messages in rapid succession to the MTU that alternate between indicating that the route is available and indicating that the route is not available to cause the MTU to flush the stored MAC address information. Using either of these techniques, data packets traveling over the link may be lost and the customer sending or receiving the data packets may be adversely affected. Further, services running on the same link but not affected by the network error may be disrupted by bringing down the link or by the link flapping.